The synthesis and degradation of glutathione and the coupled uptake and release of amino acids from gamma-glutamyl linkage are controlled by a series of enzyme catalyzed reactions that are integrated into a cyclic process called the gamma-glutamyl cycle. Recent studies have shown that the enzymes of the gamma-glutamyl cycle are concentrated mainly in the choroid plexus and in brain capillaries and thus may function in transport processes between blood and brain and between cerebrospinal fluid and blood. We therefore propose to study the uptake of amino acids and the specificity of uptake in isolated brain capillaries and in the choroid plexus. The relationship of glutathione to the amino acid uptake process will be studied under several experimental conditions. Thus the uptake will be measured in brain capillaries and in choroid plexuses that have been depleted of intracellular glutathione by the administration of an inhibitor of glutathione synthesis and in preparations in which intracellular glutathione will be replaced by its analog, opthalmic acid. The effects of the depletion of glutathione in brain capillaries and choroid plexus on the in vivo amino acid uptake by the brain will also be explored. The specificity of amino acid uptake by brain capillaries and choroid plexus will be compared with the amino acid specificity of gamma-glutamyl transpeptidase, the key membrane bound enzyme that mediates the interaction of glutathione with amino acids. The involvement of gamma-glutamyl transpeptidase in the transfer of amino acids will be tested by using inhibitors of the enzyme and studying their effect on the uptake process. The mechanism of the convulsive action of methionine sulfoximine will be further explored with respect to its inhibition of glutathione synthesis in the choroid plexus and brain capillaries and the effect of this inhibition on brain amino acid uptake. Studies will be continued on the mechanism of the convulsive action of allylglycine, an analog of cysteine that is likely to interfere with glutathione synthesis or the metabolism and transport of sulfur containing amino acids.